Sorry to bring back nightmares but remember when manny would have players just guarding an open field of grass? Its basically that, players get the call and just drop to their assigned zone no matter what the receivers are doing
Match coverage is pattern matching to where the players have rules based on what the receiver does. So it could essentially turn into man coverage
Easy way to visualize it is by looking at a play art of a zone coverage, in this case this is Cover 3.
Spot dropping, you may also hear it referred to as country cover 3 if it is cover 3, just means these defenders drop to these zones no matter what if it is a pass play. If a WR comes into your zone, guard him and then pass him off as he exits and heads towards another zone.
It's how zone defense used to work decades ago. Teams still run it at times, including us, because it allows you to keep eyes on the QB at all times, but the "newer" way of running defenses these days is called pattern matching which can get complex with all sorts of rules.
To keep it simple, patter matching basically takes a traditional zone play and can switch to man coverage on the fly if the receivers run certain routes. For example, in a typical cover 3 zone, the outside CBs will play their deep third zones as we can see in the graphic. The safety plays the deep third in the middle.
If we were running cover 3 match, which is cover 3 with pattern matching rules, then the outside CBs would be reading the release of the furthest outside receiver on their side of the field. If that receiver released vertically, meaning they ran upfield for 7-10 yards(it varies by system at times) without breaking inside or outside, then that CB will switch to man coverage on that WR and follow him everywhere the rest of the play.
If that WR was to run a slant route instead, so he goes upfield 2-3 yards and cuts inside, then the corner would usually make some sort of audible call to pass him off to the defender underneath and inside of him and the corner would drift back into his normal third looking for any receiver that may come his way.
Pattern matching can get more complex than that, but that's the simplistic way of viewing it. Hopefully I didn't complicate it too much.